Patent GB-1307334-A (GB)
Title: Apparatus for analog-to-digital conversion of physical values and  their ratios
IPC: G06J1/00
Filed: 1970-07-07
Abstract: 1307334 Electric measurement PENZENSKY POLITEKHNICHESKY INSTITUT 7 July 1970 32831/70 Heading G4A The Specification describes apparatus for converting to digital form various physical values, e.g. time intervals, electric pulse durations, electric frequencies, phase shift angles of two waves and ratios of time intervals. In the embodiment of Fig. 3 for measuring a time interval t x  defined by the interval between two pulses, a coarse counter 25 counts n 0  pulses of period T 0  from an oscillator 23 between the two pulses to derive the coarsest digit. The second pulse enables an oscillator 26 which delivers pulses of period T 0 -.1T 0  to a comparator 28, the comparator receiving on its other input pulses of period T 0  and length . 1T 0 . A second counter 34 counts n 1  pulses from oscillator 23 between the second pulse and a pulse produced by the comparator 28 at coincidence of its two inputs to derive a second digit. The comparator output enables an oscillator 26 delivering pulses at period T 0 -.01T 0  to a comparator 28, the comparator receiving at its other input pulses of period T 0  and length .01T 0 . A third counter 34 counts n 2  pulses from oscillator 23 between the two outputs of comparators 28, 28<SP>1</SP> to derive the third digit, this process being repeated a number of times dependent on the required accuracy. The interval t x  is then represented by T 0  (n 0  + .1n 1  + .01n 2 + ... ). In the embodiment of Fig. 4 for measuring a frequency f x  of period T x , to derive the most significant digit a counter 25 counts cycles of the input frequency, after shaping in a shaper 35, for a time interval T 0  defined by an oscillator 36. At the end of the interval T 0  an oscillator 38 is enabled to deliver pulses of period .9T x  to a comparator 28. The comparator receives on its other input pulses of frequency f x  and length .1T x . Counter 34 counts pulses of frequency f x  between the end of the interval T 0  and a pulse from comparator 28 representing coincidence of its inputs to derive the second digit. The third digit is derived in counter 34 by counting cycles of the frequency f x  between output pulses of comparators 28, 28<SP>1</SP> the latter comparing pulses of period .99T x  from oscillator 38<SP>1</SP> (enabled by the output of comparator 28) and pulses of frequency f x  and of length .01T x . The apparatus may be modified (Fig. 5, not shown) to measure the ratio of two time intervals in which one of the time intervals is used to define the interval T 0  and pulses representing the output time interval are applied to the input of the shaper 35. It may also be used to digitize the phase shift angle between two signals of frequency f x  and period T x  by utilizing the time interval which determines the phase shift as the interval T 0 . If the oscillators 38, 38<SP>1</SP> are selected to be of periods 26/36T x  and 35/36T x  respectively the counts in the counters will represent degrees. The apparatus may also be used to digitize the ratio f2/f1 of two frequencies by using as the interval T 0  the period of the frequency f 1  of the divisor. It may also be used to measure the deviation of a frequency from a rated frequency by utilizing one period of the rated frequency as the interval T 0 . In a modification (Fig. 6, not shown) of Fig. 3 in which the counters (34, 34<SP>1</SP>) ... count pulses from their associated oscillators (26, 26<SP>1</SP>) ... when comparator (28) is triggered an oscillator 50 provides the strobing pulse of length slightly greater than T 0  (the period of oscillator (23) to a gate (52), the gate receiving at its other input the pulses from oscillator (23) of period T 1 . At equality of the gate inputs, oscillator (26<SP>1</SP>) in the next stage is enabled and gate (32<SP>1</SP>) opened to pass pulses from the oscillator (26<SP>1</SP>) to the counter (34<SP>1</SP>) until comparator (28<SP>1</SP>) is triggered. The comparator output additionally triggers oscillator (50<SP>1</SP>) which feed a pulse of length slightly greater than T 1  to the next stage controlling via gate (52<SP>1</SP>) the oscillator (26<SP>11</SP>). The process is then repeated in subsequent stages.